When a manufacturer releases a B version of an existing product the differences between the old and the new are usually small. Not so in the case of Atmel’s ATmega328P, the processor at the heart of the Arduino Uno R3. The B-type of this MCU has so many extra features that a new revision of the R3 is justified. Enter the Elektor Uno R4. The most striking difference between the Elektor Uno R4 and the Arduino Uno R3 are the four extra pins on the “power” connector and its second USART. Yes, you read that right: the Elektor Uno R4 has two USARTs making debugging and program development so much easier! Furthermore the Elektor Uno R4 has a 4-bit port E, a second I²C port, a second SPI port (four SPI ports if you count the USARTs), two additional analogue inputs, an output for the Analogue Comparator, nine PWM channels, two extra 16-bit timers, an Output Compare Modulator (OCM) and thanks to its Peripheral Touch Controller (PTC) every I/O pin can now be used as touch-s...